A fuel cell system is increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Such a fuel cell system is disclosed in commonly owned U.S. patent application Ser. No. 10/418,536, hereby incorporated herein by reference in its entirety. A fuel cell may also be used as a stationary electric power plant in buildings, and as a portable power source in a camera, a computer, and the like. Typically, the fuel cell generates electricity used to charge batteries, or to provide power for an electric motor.
Fuel cells are electrochemical devices which directly combine a fuel such as hydrogen, and an oxidant such as oxygen, to produce electricity. The hydrogen is typically supplied by a fuel source such as a hydrogen tank, for example. The oxygen is typically supplied by an air stream.
The basic process employed by a fuel cell is efficient, substantially pollution-free, quiet, free from moving parts (other than an air compressor, cooling fans, pumps and actuators), and may be constructed to yield only heat and water as by-products. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells, depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack, with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications.
Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example. The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA).
In a typical PEM-type fuel cell, the MEA is sandwiched between “anode” and “cathode” diffusion mediums (hereinafter “DM's”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper, for example. The DM's serve as the primary current collectors for the anode and cathode as well as provide mechanical support for the MEA. The DM's and MEA are pressed between a pair of electrically conductive plates which serve as secondary current collectors for collecting the current from the primary current collectors. The plates conduct current between adjacent cells internally of the stack in the case of bipolar plates, and conduct current externally of the stack in the case of monopolar plates at the end of the stack.
A valve is typically used to selectively permit and militate against the flow of a fluid therethrough. In the fuel cell system, a flow of a hydrogen gas from a source of hydrogen gas to the fuel cell stack is controlled, for example. The valve typically includes a valve head and a valve body. The valve head and the valve body are normally formed from different materials, one material being harder than the other. When the valve is in a closed position and the valve head abuts the valve body to form a substantially fluid tight seal therebetween, the softer material may be deformed. If this deformation is reversible, it is referred to as elastic deformation. If the deformation is not reversible, it is referred to as plastic deformation. Plastic deformation is undesirable because it may permit leak to develop between the valve head and the valve body.
Prior art valves include softer materials formed from an elastomer, such as ethylene propylene diene monomer rubber or fluoroelastomer, for example. The elastomers are limited to use at temperatures above −40° C. However, in fuel cell applications where hydrogen is used, for example, lower temperatures such as −80° C. can be experienced. Accordingly, elastomers cannot be used. At the lower temperatures, plastic materials such as polyetheretherketone or polytetrafluoroethylene are used. These materials accommodate a certain elastic deformation, which is useful for facilitating the substantially fluid tight seal between the valve head and the valve body. However, use of these materials also creates a possibility for an amount of plastic deformation, which is undesirable.
It would be desirable to produce a valve for use in a fuel cell stack, wherein the valve includes an elastically deformable component that is elastically deformed when the valve is in a closed position, and a plastic deformation of the valve is minimized.